Add unique!(f, itr)

[fredrikekre]

We have a unique(f, itr):

  unique(f, itr)

  Returns an array containing one value from itr for each unique value produced by f applied to
  elements of itr.

but no corresponding in-place version, would be nice to have. See #20619

[bvsravikiran]

Can I work on this issue?

[fredrikekre]

Yes, anyone can work on any issue.

[deepaknalore]

@bvsravikiran If you are not working on it. I would like to pick it up

[bvsravikiran]

Sure. Go ahead.

…

On Fri, Aug 17, 2018 at 01:41 des2 ***@***.***> wrote: @bvsravikiran <https://github.com/bvsravikiran> If you are not working on it. I would like to pick it up — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#28415 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AGtPGga8QfXlZkG2aoVZURx7B-BW1MIdks5uRmWHgaJpZM4VtIdO> .

[shaktee]

Yikes. I was unaware that someone was working on this. I had already done this because I needed it. So, I created a pull request for it #28737

[shaktee]

If it is not the best implementation, please feel free to discard the pull request. (But, I would appreciate a commentary on the things that need improvement.)

[raghav9-97]

If I am understanding it correctly, the return values of unique!(f, itr) does not really care about original order of occurrence.As it is also clear from the documentation of unique (f itr) :

unique(f, itr)

Returns an array containing one value from itr for each unique value produced by f applied to elements of itr.

Ex- A = [1,-1,3,-3,5,-5]

The unique!(f, itr) can generate -1,-3,-5 (if sort!(A) and _groupedunique!() like function applied) as well as 1,3,5 if order of occurence is necessary.

[StefanKarpinski]

I think we generally want to leave the elements in their original order. There's no reason not to do so.